An elevator comprises an elevator hoisting machine into which a machinery brake is implemented. The machinery brake engages mechanically with a rotating part of the hoisting machine causing the braking effect. The machinery brake may e.g. be a shoe brake, a drum brake or a disc brake.
A structure of the machinery brake is typically such that it comprises an armature part provided with a brake pad and a frame part comprising an electromagnet. Between the armature part and the frame part is arranged one or more springs. The operation of the machinery brake is based on a utilization of the springs that are arranged to push the armature part provided with a brake pad against the braking surface of a rotating part of the hoisting machine in order to achieve the braking effect i.e. holding the elevator car stationary in the shaft when the control of the motor is inactivated. By means of the electromagnet when provided with an electric current it is possible to pull a magnetic core of the armature part, and thus the armature part, against the spring force of the springs so that the brake may be released away from the braking surface. Hence, the control of the machinery brake between the activated and inactivated states may be achieved by controlling the current supply of the electromagnet and, thus, the force of attraction of the electromagnet may be controlled.
As is clear the machinery brake of an elevator hoisting machine is under heavy forces when used. Additionally, the elevator is affected by great number of environmental variables, such as constant change in load, vibration caused by the hoisting motor among others, thermal expansion due to ambient temperature and temperature generated by elevator operation. All these have also effect on elevator brake and the elevator parts in general and in the worst case may cause displacement of parts even so that the elevator starts to misoperate or stop operation in full. As regards to elevator brake it is important to detect that the brake parts have such mutual positions that they do not prevent the operation of the elevator brake.
In known solutions so called micro switches are used for detecting mutual positions of at least two objects, and especially a change in positions of the objects. However, the problem in the use of micro switches is that they cannot be used in every application areas because there is no possibility to arrange a space for them and/or the operational environment is such that it prevents the use of the micro switches. For example, an electromagnetic field of the electromagnets may cause challenges in using the micro switches, which is the case in elevator brakes. Moreover, one problem with micro switches is that they are unreliable by default and their accuracy is inadequate in many application areas. For example, in elevator brakes the mutual motion of the armature part and the frame part is in scale of 0.15 mm, but the micro switches cannot detect such a small motion with acceptable reliability. Further, manufacturing of the micro switches is challenging.
Hence, there is need to develop solutions by means of which it is at least partly possible to improve a monitoring of an operational state of elevator brakes.